Systems for providing goods or services by means of electronic memory cards comprise cards held by users and read/write devices associated with the machines for providing goods or services. In order to obtain goods or service, the user inserts a card into the read/write device so as to enable the device to verify that the card does indeed give access to the goods or services under consideration, and so as to modify the balance contained in the card as a function of the goods or service provided. Under some circumstances, the reader can also be used to verify that the cardholder is the legitimate card owner.
Memory cards are of the prepaid type, i.e. in order to obtain the right to use a card, the user must initially pay the organization providing the goods or services an amount of money which is not less than the amount required to obtain the goods or services authorized by the card. It is therefore tempting for a dishonest person to make a card having the same electronic circuits as a genuine card and containing the same information and/or programs as a genuine card.
Although it is possible to take a genuine card and determine its geometrical characteristics and identify the nature of the circuit it contains, it is, in contrast, impossible or quasi-impossible to determine the information and the programs contained in the circuits in such a card, and in particular it is practically impossible to determine how information progresses during utilization of the card by virtue of the dialog which then takes place between the read/write device and the circuit in the card.
One way for a dishonest person to solve this problem consists in acting directly on the read/write device. To do this, a "fake" card having the same geometrical characteristics and the same external contacts as a genuine card is inserted into the read/write device, but the circuit in the fake card is replaced by conductors which are embedded in the card body and which are connected to contacts external to the card and lying outside the read/write device. The other ends of these wires can the be connected to powerful data processing means capable of receiving and analyzing the electrical signals generated by the read/write device and capable of simulating the signals normally emitted by a card until the entire information interchange procedure has been reconstituted.
In order to counter this attempt at dishonest use, proposals have already been made in French patent number 2,554,262 granted May 18, 1987, to provide the reader device with means for detecting the presence of extraneous conductor wires inserted into the read/write device.
The object of the present invention is to provide an improved embodiment of a read/write device provided with such a detector device.